Field of the Invention
The invention relates to an electronic circuit breaker with a semiconductor switch, the source connection and drain connection of which are connected between a voltage input and a load output, and the gate connection of which is connected to a control unit, which is supplied at the input end with a signal representing the load current.
Description of the Background Art
An electronic switch or circuit breaker of this type is known, for example, from DE 203 02 275U1. The electronic switch has a semiconductor switch in the form of a MOSFET (metal-oxide-semiconductor field-effect transistor), which is connected in a current path between an operating voltage connection and a load connection. To achieve reliable current limitation in a direct voltage network, a measured value, detected by a current sensor in the current path, is supplied to a comparator input of a control device. When a switch-on signal is present and at a measured value that falls below a reference value, the control device biases the semiconductor switch into conduction, whereas at a measured value that exceeds the reference value, the control device biases the power transistor to cut-off and limits the current flowing across it to the reference value.
A power distribution system in the low-voltage range, in particular, in the 24 V DC range, having a number of circuits each having an electronic circuit breaker as short-circuit protection and/or overload protection, is known from EP 1 186 086 B1, which corresponds to U.S. Pat. No. 6,490,141, which is incorporated herein by reference. The circuits are jointly supplied by a clocked power supply unit. In the event of an overload when an adjustable threshold is exceeded, e.g., by 1.1 times the rated current (IN), the electronic circuit breaker is switched off after the delay time has expired, whereas in the event of a short circuit, a current limitation occurs first and after a further threshold (e.g., 2×IN) is exceeded, the circuit breaker is switched off after a specific turn-off time has expired.
An electronic circuit breaker, which is triggered by a microprocessor via a trip circuit and interrupts the power supply to a load with a time delay, is known from EP 1 150 410 A2, which corresponds to U.S. Pat. No. 6,356,423. A partial interruption of the circuit breaker occurs beforehand or simultaneously.
A partial interruption of an electronic circuit breaker with a plurality of switch blocks, each of which have an electronic switch in the form of a MOSFET and a comparator controlling it via a joint microprocessor, is also known from EP 1 294 069 B1, which corresponds to U.S. Pat. No. 7,230,813. In the case of an overcurrent, the power supply to the load is interrupted after a time delay, which follows a partial inhibition of the at least one switch.
The semiconductor switch of the electronic circuit breaker is utilized as a constant current source for charging the capacitor for switching particularly capacitive loads and/or for the protection thereof from overcurrent and short circuit. The semiconductor switch and in particular a MOSFET employed hereby must be able to support the power dissipation as a result of the inrush current during the switching or during the charging of the capacitor. Because of this situation, electronic circuit breakers, in particular those with a constant current limitation, are usually designed with an overdimensioned semiconductor switch (MOSFET) to adequately take into account this power dissipation. A dimensioning of this type of employed semiconductor switch leads to increased expenditures, however, and a correspondingly large space requirement within the circuit of the electronic circuit breaker.
An alternative option is to undertake a clocked driving of the semiconductor switch by means of pulse width modulation (PWM). However, this increases not only the driving outlay. Rather, PWM driving leads to problems in the case of inductive loads.